Wednesday, 5 September 2012

Outline of Cell Theory

The invention of microscopes in the 17th century lead to the discovery of cells: Robert Hooke first coined the term 'cell' after observing the structure of cork and other plant tissues in 1655.
In 1674 Anton van Leeuwenhoek made the first observation of single-celled organism (microorganisms)And in 1838 Schleden and Schwann developed the Cell Theory:
  • Cells are the smallest unit of life and nothing smaller can survive independentally
  • All living things are made of cells
  • Existing cells have come from other cells

(Source: , IB Biology Course Companion)

Saturday, 17 March 2012

5.20 Cloned transgenic animals

Evaluate the potential for using cloned transgenic animals, for example to produce commercial quantities of human antibodies or organs for transplantation.

Animals which are cloned are genetically identical and transgenic refers to an organism having DNA from two or more organisms.

Commercial production of antibodies (example using transgenic cows):

  1. We want to obtain an egg cell from the cow, and from a human we will take a cell and we are going to remove using restriction enzymes we are going to cut a gene associated with antibody production. 
  2. In the egg cell we knock out the cow antibody gene and then we are going to add the human gene using ligase enzyme. 
  3. The cow cell is then developed by mitosis to form clone of cells - an embryo. 
  4. This is transferred to a surrogate mother which will then produce genetically identical calves and in this particular example, the gene for antibodies is expressed and the human antibodies are collected from the milk of the animal in a large commercial scale.

5.19 Mammal Cloning

Describe the stages in the production of cloned mammals involving the introduction of a diploid nucleus from a mature cell into an enucleated egg cell, illustrated by Dolly the sheep

The original sheep in which the scientists take the genetic information from would have the same genes as its clone (Dolly).  This is done by:
  • Removing a diploid cell with the full set of genetic information. This nucleus contains all the genetic information to form a clone.
  •  At the same time, we need to obtain a cell, which has a tendency to divide, so another sheep would be injected with hormones to produce eggs, but we don't want the genetic information so we remove it (enucleation). 
  • So we take the cell with the genetic information that we do wish to copy and we take the egg cell which divides and we fuse them together and by doing so we combine the genetic information that we want with a cell that needs to divide
  • The combination of the two results in many cell divisions by mitosis and forms a ball of cells called the blastula, and this is essentially an embryonic sheep
  • This embryo is placed into another sheep - the surrogate sheep.
  • The embryo will grow into a foetus and then it will be born and this sheep that is born is called Dolly and it has the same sets of genetic information as the first sheep

Sunday, 11 March 2012

5.18 Commercial Plant Growing

Understand how microprogation can be used to produce commercial quantities of identical plants (clones) with desirable characteristics.

If a plants has commercially desirable characteristics, people would want to make many copies of it, however, the two ways of doing this:

  • Sexual reproduction will lead to variation and a loss of qualities. 
  • Therefore, we want to use cloning technique (micropropagation) so that we get many plants of the same quality and commercially that keeps the product the same so it can be sold.

5.17 Micropropagation

Describe the process of micropropagation (tissue culture) in which small pieces of plants (explants) are grown in vitro using nutrient media.

We begin with a plant which has characteristics that we consider desirable and we want to produce more plants of the same kind, the problem is if we use sexual reproduction, the plant will show genetic variation, instead we will have to cloning technique called micropropagation.

  1. We begin by taking tissue from the shoot tip or the root tip 
  2. The next step is under aseptic conditions (free from contamination), we are going to cut this tissue into many small parts
  3. Then transfer the tissue to a petri dish which will contain nutrient agar.
  4.  In addition to the minerals, there will also be rooting compounds and other plant hormones which will encourage the growth of each of the small parts into small clone of the original plant and then each of these can be then grown on into a seedling.
  5.  In the process of doing so, we create a lot of copies of the original plants, and these plants are known as 'clones' which will have the same genes.

5.16 Transgenic Organism

Recall that the term 'transgenic' means the transfer of genetic material from one species to a different species.

The previous objectives 5.13 and 5.15 both show examples of transgenic organisms:

  • In 5.13, the bacterial cell had become transgenic since it still had bacterial DNA but also plasmids that carried human insulin genes.
  • In 5.15, the maize had  become transgenic since we introduced the BT gene to the maize DNA.

Saturday, 3 March 2012

5.15 Genetically Modified Plants

Evaluate the potential for using genetically modified plants to improve food production. (illustrated by plants with improved resistance to pests)

In this example, we will use the crop maize:

  • Maize is damaged by the larvae of the european corkborer and can cause up to 20% loss of crop yield.
  • The bacterial Bt has a chromosome which contains a gene which produces Bt toxin and is known to kill the cork borer larvae.
  • The first step is to take the restriction enzyme to the gene of the Bt bacterium and chop the gene out so we have the Bt gene for the toxin, this is then transferred to the cells of the maize plants.
  • The technique involves the process which is known as 'gene gun' which involves taking tiny particles of gold and coated in the Bt gene, which is fired at high velocity at the plant cell and introduces the Bt gene to the interior of the plant cell.
  • So the plant cell gets the genes, so the maize cells have the Bt genes and means when it is switched on it produces the Bt toxin and kills the pests (larvae of cork borer) and increases crop yield

5.14 Humulin

Understand that large amounts of human insulin can be manufactured from genetically modified bacteria that grow in a fermenter.

  • The bacterial cell containing the recombinant DNA with the human genes (in this case the production of insulin) can be injected into a fermenter and will be necessary to provide it with nutrients, control the temperature and pH and also the gases. 
  • By creating the optimal temperature for bacterial growth, we will see population increase and see the bacteria manufacture protein insulin. 
  • The bacteria inside the fermenter will manufacture the insulin protein from the nutrient (amino acids) provided in the fermenter and it will be necessary to remove the product and carry out purification (called downstream processing) for human usage.
  • The genetically engineered human insulin is called humulin

5.13b Hosting recombinant DNA

Describe how plasmids and viruses can act as vectors, which takes up pieces of DNA, then insert this recombinant DNA into other cells.

  1. After the recombinant DNA is formed, it is necessary to find a host cell for it. In this instance, we will use the virus to achieve this.
  2. We have to remove the nucleic acid from the virus, leaving us with the capsid of the virus alone.
  3. The plasmids are taken up by the virus and the virus will act as a vector of the recombinant DNA.
  4. It will help us transfer that DNA to our host cell, the virus known as a phage infects bacterial cells, and so the virus is able to attach to the cell membrane of the bacteria and insert the recombinant DNA into our host cell.
  5. At the end of this process, we will have a bacteria containing the recombinant DNA including the human DNA for insulin

5.13a Recombinant DNA

Describe how plasmids and viruses can act as vectors, which take up pieces of DNA, then insert thiis recombinant DNA into other cells.

Plasmids are find in bacterial cells and are a ring of DNA and are particularly small carrying little DNA.

Viruses have a protein shell called a capsid and inside there would be a Nucleic acid (of which contains either DNA or RNA).

The human chromosome is made of DNA and in our example, we will talk about the gene which codes for the production of the protein, insulin (hormone controlling blood sugar levels).

  1. The restriction enzyme would be selected to cut the DNA, leaving us with the gene of insulin separately.
  2. Having cut the gene, the plasmid will also be cut with the same restriction enzyme.
  3. This leaves the plasmid ring structure broken, the human insulin gene is then inserted into the plasmid.
  4. This will leave our plasmid with the human gene inserted and is then necessary to apply ligase enzyme which will join the DNA.
  5. This combination of the human gene, and the plasmid is known as recombinant DNA.

5.12 Restriction and Ligase Enzymes

Describe the use of restriction enzymes to cut DNA at specific sites and ligase enzymes to join pieces of DNA together.

  1. The restriction enzyme is able to cut the DNA, the restriction enzyme cuts the DNA at a particular location, and this location is identified by the base sequence
  2. The ligase enzyme is able to join the two pieces of DNA together.

These are commonly used with genetical engineers and bio engineers.

Saturday, 25 February 2012

5.11 Breeding Animals

Understand that animals with desired characteristics can be developed by selective breeding.

Lets use cow as an example:
In this case the desired outcome for the cow is the milk yield. The earliest farmers would realise a few cows would be producing 50 ml of milk, while some produces 150 ml of milk, however, most of the cows would be producing 100 ml of milk.

The farmer will collect all the milk but he will only choose to cows which produce 150 ml milk as the breeding cows. In the next generation we find that a few cows are producing 100 ml, a few cows are producing 200 ml and the majority of cows will be producing 150 ml of milk.

He will then select the cows which produce 200 ml milk as the breeding cow. And in the next generation there would be a few cows producing 150 ml of milk, a few producing 250 ml of milk and the majority producing 200 ml of milk.

This shows that the milk yield would be genetic which means that the farmer can select the one with the desired characteristics to breed.

5.10 Breeding Plants

Understand plants with desired characteristics can be developed by selective breeding.

Lets take the rice crop as an example:
The number of rice grains is under the control of genes and if the farmer wants to improve the number of rice grains per plant; he notices that some plants have 6 grains per stem while others may have 8 grains per stem or even 10 grains per stem. So the farmer's decides to harvest the 6 grain and 8 grain plant but he will use the 10 grain ones for planting/breeding.

In the next generation of plants, he noticed that the rice plants are now producing 8 grains per stem, 10 grains per stem or 12 grains per stem. So he would harvest the 8 grain and 10 grain plants and select the 12 grain ones for breeding.

In this way the grain of the rice plant gradually increases which means the yield has increased.

Wednesday, 15 February 2012

5.9 Fish Farming

Explain the methods which are used to farm large numbers of fish to provide a source of protein, including maintenance of water quality, control of intraspecific and interspecific predation, control of disease, removal of waste products, quality and frequency of feeding and the use of selective breeding.

Fish is an attractive product for farmers as they have low fat and high protein, but also that they are efficient at turning the nutrients into fish mass.

Fish farming will allow us to control the quality of water (clean), controlling the amount of predators and controlling the pests and diseases. By controlling these factors, it will result in a increase in yield of the fishes. However, where you have a high density of fish, there is a possibility that the transmission of disease will happen very fast and in some cases farmers have taken to use antibiotics which is of concern to human health. The abundance of fish within the fish farm also makes pests common and therefore some farmers will add pesticides to it which is also harmful to consumer health.


  • Aquaculture industry has provided a lot of employment opportunities
  • Fish farming may help conserve wild fish resources as it may provide a faster rate of food supply to keep up with the demand
  • Aquaculture may provide the main source of protein for people in many areas


  • The addition of antibiotics and pesticides may cause health hazards on consumers

5.8 Fermenter

Interpret and label a diagram of an industrial fermenter and explain the need to provide suitable conditions in the fermenter, including aseptic precautions, nutrients, optimum temperature and pH, oxygenation and agitation, for the growth of microorganism.

  • The industrial fermenter is the reaction vessel in which fermentation occurs, normally made out of steel or copper. Inside of the steel jacket, there is normally another steel jacket inside, and in between the two, there will be layer of water in which it will act as a cooling jacket in order to keep the optimum temperature for the reaction to occur.
  • The fermenter will need to be cleaned and there will be a inlet where steam sterilises the fermenter between two fermentations. Steam is used to clean the tanks out.
  • Within the fermenter there will be a heating plate to raise the temperature, and the combination between the heater and the cooling jacket, provides the optimum temperature for fermentation.
  • Nutrient will also be added to the tank which will act as food for the microorganism. There would be a temperature probe in the tank in order to monitor the internal temperatures and the fermentation reaction would also require the addition of the microorganisms. The pH probe is also built in the fermenter in order to keep the conditions at the optimum rate of reaction. 
  • We will also need a way to stir the reaction and this is done by the addition of motor and this will agitate the mixture preventing the mixture to slump.
  • At the end of the reaction, we need a way to drain off the product, which also leads to a process called downstream processing which involves purification of the product
So in conclusion, the fermenter is to keep the optimum growth conditions for the conditions so it will provide the product we are looking for. 

Tuesday, 14 February 2012

5.7 Yoghurt

Understand the role of bacteria (Lactobacillus) in the production of Yoghurt.

  1. Firstly, milk is obtained from cows
  2. Then, the milk is treated in order to remove pathogens such as the TB bacillus with a process called pasteurisation
  3. The milk sugars are then converted into lactic acid. 
  4. This is done by incubating the milk to about 45-46 degree centigrade with the addition of lactobacillus
  5. Lactobacillus produces the enzymes which helps to break down the milk sugar into lactic acid
  6. The acid will result in a lower ph, and this causes milk protein to solidify and this solidification of the oft the milk product is what we call yoghurt.

5.5 Beer Production

Understand the role of yeast in the production of beer.

Beer is largely ethanol, an alcohol molecule, is produced from glucose which is broken down to ethanol and carbon dioxide.

Glucose =====Anaerobic Respiration (with the aid of yeast)==> Ethanol + Carbon Dioxide

The ethanol is often flavoured with the addition of plants such as hops which is traditionally added to change the flavour. The glucose comes from starch which is converted into maltose and maltose into glucose. The starch is converted into maltose by amylase and maltose into glucose by maltase. The starch comes from barley seeds, sometimes, wheat seeds and some other types of beer, include rice. The starch is broken down to maltase through the germination of the seed, commonly known as 'malting'.

5.4b Biological Control

Understand the reasons for pest control and the advantages and the disadvantages of using pesticides and biological control with crop plants.

Biological Control:
One of the most famous biological control example was in Australia, where the prickly pear cactus (the pest)  of North America was first introduced into gardens and escaped into the countryside and flourished under the Australian climate system. The cactus started to cover a good deal of agricultural land and was necessary to get rid of it, however, there was no natural herbivore of the cactus so an alien specie (non-native specie) was introduced from another country which was a moth (Cactoblastis). This moth was introduced and had no competitors so they started to remove the prickly pear cactus.


  • No toxic chemicals involved
  • Less impact on man or the impact

  • Not 100% effective
  • Often difficult to control, there is often a danger that the alien specie would start preying on native species, causing native specie population to diminish
  • Difficult to match a predator to the prey which can effectively remove the pest
  • This process may last a long time

Monday, 13 February 2012

5.4a Pesticides

Understand the reasons for pest control and the advantages of using pesticides and biological control with crop plants.

Large fields of crops of the same type are called Monoculture. Monocultures tend to be really susceptible to pests which uses the crops as their own food source. By doing so, this reduces the productivity of the farm which reduces the amount of crop yield and has an financial impact on the farmer as less is produced.
To overcome this, one of the solutions is to use pesticides (chemicals used to kill the pests)


  • Pesticides are chemicals which makes it easy to obtain.
  • They are easy to apply.
  • They are very effective.

  • Many of the chemicals are toxic, they may kill other plants and animals, other than the pests which may be harmful to humans as well.
  • Bio accumulation is where the pesticides build up through the food chain causing problems for animals in the higher trophic levels. 
  • Mutation in the pest often lead to resistance so the pesticide will need to be applied at a higher level, in some cases, the pests have complete resistance to the pesticide and so the farmers have to find an alternative pesticide.

Saturday, 11 February 2012

5.3 Fertilisers

Understand the use of fertiliser to increase crop yield.

Farmers normally add fertilisers (mostly in the form of nitrates or phosphates) to the soil in order to help promote the growth of crops and increase yield. These nutrients are taken up by the root structure and then moved in the transpiration stream up to the leaves for the construction.

Nitrates will go up to form proteins which is then used by the plants to generate/repair cells.
Phosphate is involved in the DNA of plants and the membranes of the plant.

The fertilisers can be divided into two groups:


  • Made from animal manures (waste) on farms and often goes through the process of decomposition and fermentation and forms a slurry compound
  • This is applied to the fields to provide Nirates and Phosphates to promote growth

Inorganic (Artificial):

  • These take the form of chemicals (synthetically produced), well known ones are potassium nitrate and ammonium nitrate which can be bought by the farmers and applied to the fields
  • These will release the nitrates which will promote growth of the crops.

Consequences of using fertilisers:
  • Fertilisers may run-off due to excess rain and reach water sources of causes eutrophication. The fertilizers enrich the nutrient content in water sources which causes algal blooms where the algaes grow fast and multiply. When algae die they are broken down by decomposers, the process of decomposition uses up oxygen in the water sources and causes massive die-off of fishes.
  • Fertilisers may be hazardous to human health: for example, organic fertilisers might leach through to water sources and cause diseases such as E.Coli which is commonly found in cow manures. Inorganic fertilizers may also leach down to underground water sources and cause cancer and is toxic to humans.
  • Fertilisers are normally used in intensive farming techniques (when a farmer is trying to obtain as much as possible from each hectare of land) which may deplete the original soil nutrients.

5.2 Crop Yield

Understand the effects on crop yield of increased carbon dioxide and increased temperature in glasshouses.

Photosynthesis: Carbon Dioxide+Water===Light & Enzyme==> Glucose+Oxygen

Increase in carbon dioxide (substrate) theoretically means that the rate of photosynthesis will increase, resulting in a increasing in crop yield up to a point where it reaches the optimum point of the rate of photosynthesis.
If we increase the temperature, the theory predicts an asymmetrical graph which means if we increase temperature, the rate of photosynthesis increases, resulting in an increase in crop yield. However, after the rate of photosynthesis reaches the optimum, the rate of photosynthesis starts to slow down, as some enzymes denature which decreases total crop yield.

Increase in temperature in a glasshouse can help avoid frost damage and provides constant temperature both of which contribute to an increased crop yield.

Wednesday, 8 February 2012

5.1 Glasshouses and Polythene Tunnels

Describe how glasshouses and polythene tunnels can be used to increase the yield of certain crops.

Glasshouses (a.k.a. greenhouses) are basically a small house but all surfaces are made out of glass - allowing light to penetrate through to the interior of the glasshouse.

First of all, we start with solar radiation, and that is our initial source of energy, in the form of light. The light is able to penetrate through the glass to the internal surfaces. The next feature is that the light is absorbed by surfaces inside the glasshouse, which could be soil, plants etc. These surfaces will then re-emit this energy as heat which warms the hair, raising its average kinetic energy (temperature increases).

  • The warm air which is raising the temperature is trapped and eventually all parts in the glasshouse will be warm, this warm air makes the enzyme reaction speed nearer the optimum temperature, therefore reacting faster and producing more products. 
  • As well as this, glasshouses provide shelter for the plants inside, which allow plants to survive through climatic hazards such as strong storms and winds, allowing plants to be able to mature and be harvested.
  • Since plants are in an enclosed area in the glasshouse, they are most likely to be immune to diseases and pests outside the area which protects the plant and allows it to grow. 
  • Additionally, glasshouses provide a constant temperature all year round which means a constant production which is particularly true in high altitude areas.
  • Glasshouses also prevent a loss of water vapour through transpiration which prevents the plants from drying out.
  • Plants also avoid frost damage, especially seedlings, in the spring.
  • Glasshouses are often warmed by the burning of fossil fuels, this leads to an increase in the carbon dioxide levels in the glasshouse which means more product from photosynthesis.
  • In glasshouses, through incomplete combustion, ethene may form as the product which can help stimulate fruit ripening, particularly with the tomato.

The polythene tunnels, usually a framework with polythene over the surface which also allows light to penetrate through to the interior. Even though, both polythene tunnels and greenhouses provide warm temperature for the growth of plants, polythene tunnels provide less shelter for the plants and may be less effective which may have an effect of the output. Polythene tunnels are more common in developing countries than developed countries because of the cheaper costs but sometimes is more preferred because it is more adjustable and movable.

Monday, 6 February 2012

2.89 Hormonal Responses

Understand the sources, roles and effects of the following hormones: Anti-Diuretic Hormone, Adrenaline, Insulin, Testosterone, Progesterone and Oestrogen.

Hormonal system also coordinates the body, hormones are chemicals which are produced by glands and travel to certain parts of the body through the bloodstream.

Adrenaline glands secrete adrenaline, which increases heart rate and makes the subject more alert, this is secreted when the person is nervous, frightened or angry and helps your body cope with emergencies.

ADH controls the level of the water in your body, it controls the amount of water re-absorption in the collecting duct and is produced in the pituitary gland in the brain.

Pancreas secrets insulin and the main purpose of insulin is to lower blood sugar levels. On the other hand, pancreas also secretes, glucagon which increases blood sugar level.

Testosterone is produced in the testes in males which develops male features during puberty which matures sperm cells in males.

Ovaries produce progesterone and oestrogen in females, these control the menstrual cycle and develops female features during puberty.

2.88 Skin Response

Describe the role of the skin in temperature regulation, with reference to vasoconstriction and vasodilation.

There are many different types of sensors on the skin such as pain sensors, touch sensors, pressure sensors and temperature sensors which we will focus on.

Our body keeps our body temperature constant at about 37 Degrees Celsius and thermoregulates in order to keep the body temperature in this range. This is also known as homeostasis.

If the surrounding temperature is too cold:

  • Vasoconstriction happens as capillary narrows which decreases the flow of heat to the skin
  • We stop sweating as we lose heat in this process as well
  • We shiver to increase heat production in the muscles
  • Hair erects in order to trap a warm layer of air and to avoid heat from escaping.
If the surrounding temperature is too hot:
  • Vasodilation happens where the capillary is widened which carries more blood to the surface which heat can be transferred out.
  • Sweating occurs which decreases body temperature

2.87 Eye Reponse

Understand the function of the eye in focusing near and distant objects and in responding to changes in light intensity.

Most of the bending of the light rays is done by the curved cornea but the lenses can also bend light slightly. The shape of the lens is controlled by the ciliary muscles.

When you are looking at a far object:

  • The ciliary muscles relax
  • Which tightens the suspensory ligaments
  • The lens turn into a thin shape
  • The distant object is focused on the retina
When you are looking at a close object:
  • The ciliary muscles contract
  • This slackens the suspensory ligaments
  • Elastic lens becomes fatter
  • The near object is focused on retina
image courtesy of michelle biology

If there is bright light:
  • Circular muscles contract
  • Radial muscles relax
  • Pupils become smaller and less light enters the damage (to decrease damage that can be caused by strong light intensity)
If there is dim light:
  • Circular muscles relax
  • Radial muscles contract
  • Pupil enlarges and more light can enter the eyes, which helps us see in dark places

2.86 Eyes

Describe the structure and function of the eye as a receptor.

Our eyes is the body's receptor to light and gives us the sense of sight, which most of us depend upon. It detects changes in light intensities.

At the front of the eye is the cornea where the light enters the eyes. The light then passes through the pupil which is surrounded by the coloured iris. The light focuses on the fovea and the optic nerve receives the image perceived and projects it our brains.

Parts - Functions

Cornea - allows light in and is the main refractive surface of the eye
Pupil - The pupil either dilates or contracts with the help of the iris. This controls the amount of light entering the eye so that the lens doesn't get damaged.
Iris - Muscle surrounding the pupil which helps in dilating and making the pupil smaller. The logitudinal muscles contract and the radial muscles relax to make he pupil big and vice versa.
Lens - Helps with the refraction of the light onto the retina.
Optic Nerve - Carries impulses generated by the retina to the brain and turns into vision.

Sunday, 29 January 2012

2.85 Reflex Arc

Describe the structure and function of a simple reflex arc illustrated by the withdrawal of a finger from a hot object

In this example of the reflex of withdrawing your hand from the hot object:
  • The stimulus is the hot object
  • The receptor is the heat sensor in our skin
  • The impulse travels to the spinal cord along the sensory neuron
  • In the spinal cord the impulse is passed on to the relay neuron
  • This then passes on to the motor neuron
  • The motor neuron carries the impulse to the muscle and the response is the muscle contracts to move away
(Notice how this impulse does not go through the brain first, this is because it makes the response faster and reduces further cell damage due to slow response)

Another Detailed Diagram:
Add caption

2.84 Electrical Impulses

Understand that stimulation of receptors in the sense organs send electrical impulses along nerves into and out of the central nervous system, resulting in rapid responses.

  • The messages that nerves carry are called the nerve impulses and they are electrical signals.
  • They pass along quickly along the axon of the neuron.
  • Some axons have a fatty sheath around them which insulates the axon and allows the impulse to travel faster along the axon.
Diagram showing how it works:

2.83 Central Nervous System

Recall that the central nervous system consists of the brain and spinal cord and is linked to sense organs by nerves.

  • The nervous system controls your action and coordinates different parts of the body.
  • The main parts of the nervous system are the brain and the spinal cord and together they are called the central nervous system. They are both made of delicate nervous tissue so both are protected by bones. The brain is protected inside the skull and the spinal cord is protected inside your backbone.
  • The central nervous system is connected to different parts of the body by nerves which is made up by nerve cells or neurons.
  • Sense organs are our receptors and they send messages to the central nervous system and are sent along the sensory neurons
  • When the central nervous system sends messages telling effectors what to do, the message is sent along the motor neuron

2.82 Communication

Describe how responses can be controlled by nervous or by hormonal communication and understand the differences between the two systems.

1. The part on the left of the diagram (the cell body), would be embedded in our spine and on the other end it would be connected to an effector, and in this case, the muscle fibres. The electrical impulse or the nerve impulse is carried inside the walls from the cell body to the synaptic knot where it connects to the muscles through the axon which can be as long as one meter and only one cell wide. In Mammals the axon would be surrounded by another type of cell known as the Schwann cell and these contain a great deal of fat and these form the myelin sheath. The effect of having a myelin sheet is that it increases the speed of nerveconduction and this is one way of connecting the coordinator to the effector.

Diagram of the Motor nerve:

2. The second way is known as the endocrine system. This involves the Endocrine gland which produces chemicals (hormones) which can be either protein or steroids. An example would be the adrenal gland, the adrenal gland would be secreting adrenaline to the blood which will travel through the blood stream and will arrive at the organ it affects (target tissue) and will have an effect upon it. It is possible for hormones to have multiple targets and bring about multiple effects.

Difference between Nerves and Hormones:

  • Nerve impulses are fast, Hormones normally take longer.
  • Nerve impulses re sent through neurons whereas hormones are sent through blood.
  • Nerve impulses enables body to response to external environment and the hormones enable body to respond to internal environment

Monday, 23 January 2012

2.77b Thermoregulation

Understand that homeostasis is the maintenance of a constant internal environment and that body water content and body temperature are both examples of homeostasis.

Negative Feedback lop is the control of constant conditions.
The receptor of our body is called the hypothalamus which is in the brain. It responds to a stimulus which in this case, is the temperature of the blood. Our bodies tries to maintain the body temperature to around 37-38 C. So body temperature is fed back into the brain and if the body temperature needs to be increased and decreased the changes will be made by the effectors such as our skin. The response would be an increase or decrease of body temperature and this will be fed back to the loop.

In our skin we have sweat glands but also the capillary network which allows blood to be closer or further away from the skin.

If the body temperature increases, the hypothalamus will bring around cooling effect with responses such as:
  • Sweating 
  • Increase blood flow and dilate which increases the exchange of heat to the outside with the process such as radiation and evaporation of sweat 

In a cold environment, our body temperature will fall which brings about regulation to increase body temperature:
  • Shivering 
  • Vasoconstriction 
  • Hairs raised

Monday, 16 January 2012

2.9 Effect of temperature on the rate of reaction

Understand how the functioning of enzymes can be affected by changes in temperature

There are two main principles for this topic:

  1. If we increase the temperature, then we increase the 'average' kinetic energy with the particles.
  2. If we increase the kinetic energy, then we increase the number of collisions, so therefore we will have more reactions
The particles here, in particular, are the substrates (s) and the enzyme (e)
Enzyme + Substrate => Enzyme Substrate Complex + Enzyme 
Here we are looking at temperature affects it:

At low temperatures, we will except a slower rate of reaction, but as we increase the temperature, the effect is that the kinetic energy of both e and s increase so more complexes are formed more quickly.
However, we find that we reach a temperature at which the rate of reaction decreases quite dramatically

In section A, we a increasing the average kinetic energy of both reactants e and s, so we have more collisions and more reactions. After a given temperature (section C), the rate of reaction declines really quickly, this is because the kinetic energy is changing the shape of the active site of the enzyme - so it doesn't work to produce products. This is called denatured (not killed). The peak of the curve is at a given temperature so that the maximum rate is achieved at the temperature which is called the optimum temperature.

2.77a Thermoregulation

Understand that homeostasis is the maintenance of a constant internal environment and that body water content and body temperature are both examples of homeostasis.

Where the conditions are kept the same or constant.

The temperature are kept the same or constant.

Some animals, mammals as an example, when the environmental temperature either increases or decreases the body temperature remains constant. These are homeothermic organisms and this is a process called thermoregulation. This is an example of homeostatis.

From the rate of reaction to temperature graph, we can tell that there is an optimum temperature of that enzyme in the animal. Which is why the mammals keeps the body temperature at that optimum temperature if possible.

2.76 Sensitivity

Understand the organisms are able to respond to changes in their environment.

Stimuli (changes in the environment) can be either light, temperature, pressure or chemicals, in order to detect the changes in the environment, organisms are required to have receptors and in order to respond, organisms have effectors such as muscle/glands. It is the response that ensures the organism is able to survive the changes in the environment.

Monday, 9 January 2012

2.8b Enzyme Reactions

Understand the role of enzymes as biological catalysts in metabolic reactions.

We will take C6H12Oand the presence of Oand convert this to a release of energy+CO2+H2O

In the beginning of the reaction the glucose and oxygen will place in around the middle of our graph in which the y axis indicates the energy of the substrate. The bottom line represents the energy released and the energy release is indicated by the energy drop in the graph.
However, without an enzyme to break down glucose to carbon dioxide and water we will have to input energy in order to break the bonds in glucose just like the process of combustion. So initially we will need to add energy [Energy of Activation] which could be in the form of heat or extreme ph, however, they are both damaging to human cells; our biological system has found a way to overcome the energy of activation - through enzymes.
The enzymes would combine with the glucose and oxygen to form an activated complex weakening the structure without the need of heat or extreme ph and overcome the energy of activation (shown in red line). The role of the enzyme here is to reduce the energy of activation, so we can say that it makes the reaction occur more easily or faster.

2.8a Enzymes

Understand the role of enzymes as biological catalysts in metabolic reaction.

As a catalyst, the enzyme is making a reaction faster but also under moderate conditions. Metabolic reactions refer to biological reactions taking place in the cell - building cells up and breaking molecules down.

To explain how enzymes work, here is the lock and key hypothesis:

The red structure represents in the enzyme and you will notice that it has a particular shape. It is a protein and within the molecule and there is a part of molecule (b) called the active site and this is the part of the enzyme molecule where the substrate (c) fits in and they are complimentary.When they fit together they form the structure (d) which is called a activated complex. The enzyme is able to weaken the structure of the substrate in this process.

The products (f) emerge from the enzymes but the enzymes remains unchanged by the reaction. The substrate is turned into product by the action of the enzyme. Since the enzyme is unchanged by the reaction it can react again with another substrate.

2.7 Test for Starch and Glucose

Describe the tests for glucose and starch


  1. Begin by taking glucose power and dissolve it into a test tube and add to the same test tube benedict's reagent which is blue. 
  2. Take the test tube and place it in a water bath (around about 60 - 70 degree centigrade)
  3. After just 2/3 minutes we can remove the test tube and what we would be would be a colour change from blue to orange  *In weak solutions of glucose we will see a green colour developed*
  1. Put some starch powder into a spotting tile
  2. We will then add iodine solution (brown)
  3. If we add this to the spotting tile, we would see a change from the brown colour to a dark blue/black powder

Friday, 6 January 2012

2.6 Biological Molecules

Describe the structure of carbohydrates, proteins and lipids as large molecules made up from smaller basic units: starch and glycogen from simple sugar; protein from amino acids; lipid from fatty acids and glycerol.

are made up of C(arbon)H(ydrogen)O(xygen)
The simplest carbohydrate are sugars which are monomers. The large molecules are formed through combining sugars are those such as starch and glycogen.  Starch is a straight long chain of glucose whereas glycogen is a long chain of glucose with branches. The stored form of sugar in animals is glycogen and the stored form of sugar in plants is starch.
are made up of C(arbon) H(ydrogen) O(xygen) N(itrogen)
The simple smallest molecules in protein is amino acids. The amino acids are also joined together in long chains and it is these chains we describe as proteins.
are made up of C(arbon) H(ydrogen) O(xygen)
But the story here is slighty different.
The lipids contain a small molecule glycerol and another called fatty acids. Lipids have two different types of molecules joining together to form the structure of the molecule lipid.

Wednesday, 4 January 2012

2.32 Energy Content of Food

Recall how to carry out a simple experiment to determine the energy content in a food sample.


  • Thermometer
  • Boiling Tube filled with 20 cm3 Water
  • 10 cm3 of food sample in Crucible


  1. Measure the initial temperature of the water (degree centigrade)
  2. Ignited the food source
  3. Heat the water with the ignited food
  4. Measure the final temperature of the water (degree centigrade)
Let's say our initial temperature was 20 degrees Celsius and the final temperature was 30 degrees Celsius
1 cm3 of water has a weight of 1g and in order to increase one degrees it would take 4 joules

Energy released from food per gram (J) = (mass of water (g)*temperature rise (degree centigrade)*4.2)/Mass of food sample (g)

In our case:
Energy released from food per gram (J)= (20g*(30-20)*4.2)/10
=84 J/g
So in our food there were 84 joules per gram

2.31 Villi Structure and function

Explain how the structure of a villus helps absorption of the products of digestion in the small intestine.

The inside wall of the small intestine is folded which increases the surface area. When we look at the surface of the small intestine, we see finger-like projection called villi, and each villi has its own blood supply.

We can see that in a villi there are blood vessels that bring blood supply in and blood supply out. The villi is surrounded by glucose, amino acids, glycerol, fatty acids and in the space around the villi these molecules are in high concentration. The villi increases the surface area for absorption. Villi also has a small diffusion distance meaning that the diffusion happens fast. The blood vessel's distant is also quite close to the space outside meaning the molecules can diffuse in the bloodstream fast. Because the blood is flowing in and out, the blood supply out removes the molecules which are diffused into the blood and this maintains the concentration gradient by keeping the concentration in the blood low which is maintained by the blood flow.

The small intestine helps with the absorption of the lipid, and the lacteal collect the lipids before it is returned to the circulatory system.

2.30 Bile

Recall that bile is produced by the liver and stored in the gall bladder, and understand the role of bile in neutralising stomach acid and emulsifying lipids.

In the stomach is approximately 3, due to the presence of HCL [Hydrochloric Acid], the structure below the stomach, the pancreas, produces digestive enzymes, the liver is responsible for the production of a substanc named bile and is stored in the structure called Gall Bladder. When food is released from the stomach into the small intestine, the ph is approximately 3, this stimulates the release of bile from the gall bladder through the bile duct and to pancreatic duct. So the bile mixes with the digestive enzymes. The point where the pancreatic duct reaches the food the bile has two effects: the first effect is to neutralise the stomach acid and to create a ph whih is approximately 7. This ph is the optimal ph for the digestive enzymes. The second effect of bile is that the fat molecules are broken down into smaller droplets this is a process known as emulsification. A common misunderstanding is that this is an enzyme action. The purpose of the bile breaking fat down into smaller droplets is to increase surface area of the lipid, and that means lipase enzymes can digest the lipid more quickly.

2.29 Digestive Enzymes

Understand the role of digestive enzymes to include the digestion of starch to glucose by amylase and maltase, the digestion of proteins to amino acids by proteases and the digestion of lipids to fatty acids and glycerol by lipases.

Digestive enzymes turns the insoluble food into soluble molecules which can then be absorbed in the bloodstream and then assimilated into our cells. This is promoted by digestive enzymes.

There are three types of this process:

Starch- This molecule is a long chain of glucose molecules, this is insoluble and this forms the main components of food such as rice and potatoes. Amylase is used to break down starch into two molecule structures known as disaccheride  (two molecule sugars)
Maltose- The maltose is digested by maltase into glucose, this is the soluble molecule that can be absorbed by the bloodstream.

Protein- Protein is a chain of amino acids which is broken down by proteases into their monomers - amino acids. The amino acids are then absorbed in the bloodstream and then assimilated into our cells for use.

Lipid - Lipid structure is different than that of carbohydrates and proteins. The lipase breaks the bond between Glycerol and Fatty Acids and forms the two soluble molecules.

2.28 Peristalsis

Explain how and why food is moved through the gut by peristalsis.

The important thing to remember about the gut wall is that they have muscle tissues which allows them to contract. The muscle is organised around the oesophagus, and when the muscle contracts the muscle gets shorter - this means the diameter of the oesophagus will decrease. Enters the gut and stretches the wall, this causes a reflex of the muscle behind the bolus, this contraction pushes the bolus downwards through out guts.